A centrifuge that has a vertical axis of rotation and that is intended for separating or clarifying mixtures of liquids has a drum with a skimming compartment that accommodates a skimmer for diverting a clarified or separated liquid phase. Above the skimming compartment is a blocking compartment that can be filled with a blocking fluid into which a sealing disk that is rigidly connected to the skimmer is immersed and that is intended to prevent atmospheric air from getting into the skimming compartment. The skimmer and sealing disk are positioned in the compartments at a certain distance from the rotating components of the drum. The portions of the compartments communicate with each other that are below the sealing disk and above the skimmer and are connected to a channel through which a gas that is under higher-than-atmospheric pressure can be supplied to the chambers to prevent blocking fluid from squirting out of the blocking compartment into the skimming compartment.